As optical networks have evolved, network deployments have moved from point-to-point configurations to interconnected mesh architectures with various reconfigurable components contained therein. The interconnected mesh architectures can be formed with various reconfigurable optical add/drop multiplexers (ROADMs) or other types of optical nodes. In an exemplary implementation, a ROADM can include a wavelength selective switch (WSS) and the process of adding a channel to each ROADM can include opening an associated pixel on the WSS. Of course, other implementations can be used for ROADMs. As optical node flexibility increases and the interconnected mesh architectures expand, channel addition becomes problematic especially over optical networks with multiple cascaded optical nodes. These challenges are further increased as different channels can have different A-Z paths through the network with various channels traversing different paths and multiple cascaded optical nodes. Thus, optical node and network flexibility leads to interconnection complexity.
First, to turn up a wavelength, conventional systems and methods can utilize a procedure by opening pixels in the WSS in multiple cascaded ROADM sections simultaneously or in quick sequence. However opening up pixels (or any other type of enabling scheme) without any sort of control may create significant overshoot on the wavelength being launched into the fiber, and further may insert non-linear interference to neighboring in-service wavelengths. Adding a large number of wavelengths on top of low-count in-service ones can also create significant DC power offset on the in-service wavelengths that could be traffic impacting as well.
Alternatively, conventional systems and methods can include turning up wavelengths in sequence over multiple optical nodes while setting actuator values dynamically in each optical node site in non-service affecting way following the completion of add action in upstream optical nodes. This is a sequential approach versus the aforementioned parallel approach. Few constraints have to be respected in that regard: (1) a controller in each optical node has to run in a close-loop fashion getting an updated optical power reading from an associated optical power monitor (OPM), (2) the delay between consecutive close loop controller iterations are limited by the associated OPM's scanning time to report the wavelength power and the actuator's attenuation settling time, and (3) while setting attenuation in each actuator, it has to maintain the target launch power into the fiber, or need to achieve the power of the already in-service wavelengths of similar transmitter type into the fiber. Such controlled sequential method ensures proper power settings for each section, and mitigates any impact to currently deployed channels. Plant related drifts and aging effects (e.g. Microelectromechanical systems (MEMS) based WSS pixel drifts, and pixel offsets due to aging) adds another dimension into this problem due to which the pixel or the actuators cannot be open at the target attenuation in a single step. The actuator needs to be opened at a lower attenuation setting than the target actuator settings. Otherwise an overshoot can appear while adding the new channel to the fiber that may cause non-linear interference to the neighboring wavelengths.
Hence in order to respect and overcome all these constraints, conventional systems and methods take few iterations of each WSS to achieve the power target before the wavelength shows up in-service. However due to sequential operation and timing allocation for each WSS in an optical node site, the overall service turn up time for a wavelength over multiple cascaded optical nodes becomes very much significant especially in the case layer 0 (optical layer) restoration schemes. In view of the foregoing, it is desirable to have systems and methods for faster channel additions over multiple cascaded optical nodes utilizing a parallel technique while addressing the aforementioned constraints.